Twisted lead pairs on PCB to improve common mode rejection

ABSTRACT

The invention in its main aspect comprises a printed circuit board having a bus extending along a predetermined length of a portion of said printed circuit board, the bus having a predetermined width and defining a plurality of openings therein following a predetermined regular pattern, the pattern having at least a first pair of openings positioned on a first lateral side of an imaginary line along the bus, and at least a second pair of openings positioned on a second lateral side of the imaginary line along the bus, the first and the second pairs of openings being relatively arranged so that a first lead interconnecting the first pair of openings is in a twisted pair relationship with a second lead interconnecting the second pair of openings.

BACKGROUND OF THE INVENTION

This invention relates generally to an improved printed circuit board(PCB). More particularly, this invention relates to an improved PCBhaving "twisted lends" on the PCB to improve common mode rejection.Still more particularly, this invention relates to an improved PCBhaving complementary leads located respectively on the solder side andcomponent side of the PCB to improve common mode rejection.

The use of printed circuit boards to develop complex circuits having aplurality of components is well known. Such boards are usuallysubstantially planar with a component side and a solder side, tofacilitate positioning components relative to the boards and to permitsoldering of those components into the circuit to be automated. A busproblem exists with such PCBs, however, in that when a bus structureexists on a PCB for an appreciable distance, the circuit on the PCB issusceptible to cross talk and induced noise from outside interference.Highly accurate circuits are adversely affected by such spurioussignals.

One solution that is conventional to inhibit such cross talk and inducednoise is to provide the PCB with special shielding. However, suchadditional structure is costly both from a materials and a labor pointof view, and adds to the weight of the circuit. While technically suchshielding is satisfactory, its drawbacks generally outweigh itsbenefits.

Another possible solution is to design into the circuit a common moderejection circuit which assists in removing such common mode signals andin removing induced noises electronically. However, such additionalcircuitry is particularly expensive and does not function completelysatisfactorily.

Accordingly, it remains an objective in the PCB art to develop a way toencourage a common mode rejection by circuits on the PCB, whileinhibiting inducing noise, without the use of complex and expensiveadditional components of the PCB.

It is known in the electronics art to twist pairs of leads to improvecommon mode rejection of signals on the respective pair of leads. Suchtwisting literally occurs physically in that the pair of leads is infact twisted into an interlaced pattern. It is thus another overall aimof this invention to determine whether such known structure isapplicable to PCBs.

These and other aims and objectives of this invention will becomeapparent to those of skill in this art when considered in light of thewritten description of the invention which follows taken with theaccompanying drawings.

BRIEF SUMMARY OF THE INVENTION

Directed to achieving the foregoing objectives and overcoming problemsassociated with an elongated bus structure on a PCB, an improved circuitboard according to the invention comprises a solder side and a componentside, each of which includes an elongated bus structure substantially inregister. The bus structure includes a plurality of solder points. Leadsare provided between respective pairs of such solder points wherein ahigh lead is located between a first pair of such solder points on thesolder side, and a low lead is located between said first pair of suchsolder points on the component side and oppositely directed relative tothe high lead.

A plurality of patterns for such leads are disclosed.

In providing a common mode rejection circuit on a printed circuit board,the invention in its main aspect comprises a printed circuit boardhaving a bus extending along a predetermined length of a portion of saidprinted circuit board, the bus having a predetermined width and defininga plurality of openings therein following a predetermined regularpattern, the pattern having at least a first pair of openings positionedon a first lateral side of an imaginary line along the bus, and at leasta second pair of openings positioned on a second lateral side of theimaginary line along the boss, the first and the second pairs ofopenings being relatively arranged so that a first lead interconnectingthe first pair of openings is in a twisted pair relationship with asecond lead interconnecting the second pair of openings.

The printed circuit board is further characterized in that the first andthe second leads are preferably located on opposed sides of the printedcircuit board. The printed circuit board has the first lead located on asolder side of the printed circuit board and the second lead is locatedon a component side of the printed circuit board.

In another aspect, the printed circuit board according to the inventionis in combination with the first and the second leads which respectivelyare soldered at the openings.

The printed circuit board according to another aspect of the inventionfurther includes a plurality of third leads and a plurality of fourthleads respectively in circuit with the first lead and the second leadwhereby a plurality of twisted pairs of said first and said third leadsare formed relative to said second and said fourth leads.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a representative showing of a portion of a PCB on which thetwisted lead invention is placed.

FIG. 2 is a portion of the PCB shown in FIG. 1 showing a plurality oftwisted leads on a test PCB as seen from the solder side of the board.

FIG. 3 is a view of the same portion of the PCB as seen in FIG. 2 but asseen from the component side of the board, showing the plurality oftwisted leads.

FIG. 4 is a composite view of FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an end portion of a printed circuit board (PCB) 10 arrangedto serve as a test board for representative patterns of twisted leadpairs according to the invention. Those representative patterns arearranged in consecutive rows of through holes (shown from left to right)in a representative plurality of columns, only two of which are shown.More specifically, the PCB 10 includes rows 12 to 43, which for testpurposes are substantially alike when positioned adjacent one another inthe columns 44, 45. Because of the like nature of adjacent columns, onlytwo are shown.

FIG. 2 shows the end portion of the PCB 10 of FIG. 1 with leads asconnected on the solder side of the board. Specifically, rows 12 to 14are substantially identical from a first twisted pair pattern for aplurality of through holes in the board between the inlet connectors 46(three in number) at the left side of the columns 44 and 45 and theoutlet connections 47 at the right side of the columns 44 and 45.Representatively sixteen of the through holes are shown, designatedgenerally as "pins" a to p. On the solder side therefore, a lead isconnected to pin b, between pins b and c, between pins d and e, betweenpins f and g, and so forth. The twisted pairs to those connections isshown in FIG. 3 where the leads are connected between pins a and d, cand f, and so forth. The composition pattern can be seen in FIG. 4.

A second twisted pair pattern is shown in rows 15, 16, and 17, havingten pins a to j, wherein a lead on the solder side as seen in FIG. 2 isconnected to pin a, and respectively between pins b and c, d and e, fand g, h and i, exiting from the column at pin j. As seen in FIG. 3,showing the component side, a opposing lead pair is connected to pin b,between pins a and d, between pins c and f, between pins e and g,between pins g and i, and out from the column at pin h. As seen in FIG.4 in which the leads of FIG. 3 are whown as dashed lines, the opposedleads cross over each other to form the twisted pair between pins b andc, d and e, f and g, and h and i.

A third twisted pair pattern is shown in rows 18, 19, and 20 as seen forthe solder side in FIG. 2, for the component side for FIG. 3, and forthe twisted pair in FIG. 4.

A fourth twisted pair pattern is shown in rows 21, 22, and 23, while afifth twisted pair pattern is shown in rows 24 and 25. A sixth twistedpair pattern is shown in rows 26 and 27, a seventh twisted pair patternis shown in rows 28 and 29, an eighth twisted pair pattern is shown inrows 30, a ninth twisted pair pattern is shown in rows 31, 32, and 33,and a tenth twisted pair pattern is shown in rows 34 and 35. For eachpair, the pattern shown for the respective rows on the solder side isshown in FIG. 2, the pattern shown for the component side is shown inFIG. 3, and the twisted pair pattern is representatively shown in FIG.4.

Thus, according to the invention, an elongated bus structurerepresentatively shown as a row on the PCB 10 extends for apredetermined distance across a portion of the PCB 10. As seen in FIGS.1 to 3, through holes traversing the thickness of the PCB 10 arearranged on either side of an imaginary line traversing the elongatedbus. Leads connected between respective pairs of through holes arearranged on opposite sides of the PCB 10 to form a twisted pair ofleads, thus to form "twisted lands" on the PCB in order to improvecommon mode rejection performance of audio signals on the PCB.

By "twisting" the balanced bus layout on the PCB 10, the command moderejection of the summing devices connected to the board may be utilizedto its fullest. The arrangement is similar to using twisted pair cablesfor microphone inputs or for long audio feeds. By the arrangement, anyinduced noise from above or below the PCB is evenly distributed to thebus lands. This in turn provides matched inputs to the summingamplifier.

At present, it appears that the "twist" required for the best commonmode rejection on a PC board currently is a PC board having a uniformcrossing pattern for the respective twisted pairs which are slightlystaggered relative to the next bus set of twisted patterns.

These and other features of this invention will be apparent to thoseskilled in the art and the scope of the invention is determined by theclaims.

What is claimed is:
 1. A printed circuit board, comprising:asubstantially planar circuit board having a first surface and a secondsurface on the opposite side of said first surface; a plurality of busstructures extending along a horizontal length of a portion of saidcircuit board, said bus structures comprising a plurality of throughholes arranged successively at predetermined intervals along saidhorizontal length, with each successive through hole being offset in avertical direction by a predetermined distance, wherein each successivepair of through holes in each bus structure, starting with a firstthrough hole and a next, second through hole, is connected by aconductive lead formed on said first surface, and each successive pairof through holes in each bus structure, starting with said secondthrough hole and a next, third through hole, is connected by anotherconductive lead formed on said second surface, whereby a twisted pairstructure is defined by each bus structure; wherein a distance betweensaid predetermined interval for at least one of said plurality of busstructures differs from that of one or more others of said plurality ofbus structures.
 2. The printed circuit board as set forth in claim 1wherein said first surface is adapted to receive circuit componentsthereon.